In a typical gas turbine engine, a compressor having alternating stages of rotating and stationary airfoils is coupled to a turbine, which also has alternating stages of rotating and stationary airfoils. The compressor stages decrease in size to compress the air passing therethrough. The compressed air is then supplied to one or more combustors which mixes the air with fuel and ignites the mixture. The expansion of the hot combustion gases drives the stages of a turbine, which is coupled to the compressor to drive the compressor. The exhaust gases can then be used as a source of propulsion or in powerplant operations to turn a shaft coupled to a generator for producing electricity.
Blades used in compressors and turbines can have a variety of shapes and sizes depending on the operating conditions. One feature commonly found on large blades is a shroud. The shroud is essentially a platform extending outward from the airfoil at a distance along the airfoil or at the tip of the airfoil. Shrouds can help dampen any vibrations in the airfoil that occur during operation that are at least in part due to the size of the airfoil.
In operation, the shrouds of the blades are known to wear to varying degrees due to shroud-to-shroud rubbing and mechanical loading. Furthermore, the blade can deflect in the axial and tangential directions as well as twist. That is, the blade, including the airfoil and attached shroud, have plastically deformed during engine operation from their originally-manufactured state.
Blades can often be repaired and reused, often as all parts from one engine or a set. Prior repair techniques have attempted to repair shrouds to original manufactured dimensions and by doing so have not accounted for the deformation the blade has undergone during operation, thereby resulting in more extensive blade repairs and the potential to change the dimensional relationship of the mating surfaces relative to the airfoil.